Electric potential sensor

Abstract

The present invention provides an electric potential sensor for the measurement of potentials non-invasively. The sensor comprises at least one detection electrode arranged for capacitive coupling with a sample under test and for generating a measurement signal, and a sensor amplifier adapted to receive the measurement signal as input and to supply an amplified detection signal as output. Input impedance enhancing means are included for providing a high input impedance to the sensor amplifier for increasing the sensitivity of the electrode to reduced electric potentials, and a discrete pre-amplifier stage is arranged to co-operate with the sensor amplifier to reduce the input capacitance of the amplifier.

Description

TECHNICAL FIELD[0001]The present invention concerns electric potential sensors for use for the measurement of potentials non-invasively in a wide variety of applications, for example in the fields of medical diagnostics and biometric sensing.BACKGROUND OF THE INVENTION[0002]In order to create a sensitive electrodynamic measuring device, it is customary to provide a high input impedance and thereby reduce the power of the input signal required to operate the device. However, electronic circuits with a very high input impedance tend to be unstable, and so practical devices are usually a compromise between achieving the necessary degree of sensitivity, providing the desired input impedance and ensuring an acceptable degree of stability.[0003]In International Patent Application No. WO 03 / 048789, an electrodynamic sensor is disclosed in which different circuit techniques are combined to achieve several orders of magnitude improvement in sensitivity, by comparison with previously known el...

AI Technical Summary

Benefits of technology

[0009]The present invention seeks to overcome the problems described above and to provide a novel electric potential sensor which is capable of highly accurate and non-invasive signal measurement.

[0010]The present invention, at least in the preferred embodiments described below, also seeks to provide an electric potential sensor in which the signal to noise ratio is significantly enhanced.

[0015]input impedance enhancing means for providing a high input impedance to the sensor amplifier for increasing the sensitivity of the electrode to reduced electric potentials; and

[0017]According to the invention, the discrete pre-amplifier stage serves to increase the amplitude of the input measurement signal and thereby to increase the signal to noise ratio and enhance signal measurement. The discrete pre-amplifier stage may, for example, be provided by a high electron mobility transistor, or a FET arrangement.

[0021]The present invention thus aims to increase the signal to noise ratio either by increasing the amplitude of the signal or by decreasing the amplitude of the noise or both.

Problems solved by technology

However, electronic circuits with a very high input impedance tend to be unstable, and so practical devices are usually a compromise between achieving the necessary degree of sensitivity, providing the desired input impedance and ensuring an acceptable degree of stability.

Whilst these features assist in providing a sensor with high input impedance and a relatively stable operation, nevertheless, in situations where there may be weak capacitive coupling to, or a signal of small amplitude generated by, a source or sample under test, noise problems may still remain and may inhibit or prevent accurate signal measurement.

In this case, the measurement signal received by the sensor is attenuated by the capacitive potential divider formed by the coupling capacitance and the input capacitance and may be difficult to capture.

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